Cathode device



Jan. 16, 1934. F. s. MCCULLOUGHI CATHODE DEVICE Filed July 18, 1925 HHNN 'ATTORNEY Patented Jan. 1'5, i934 UNETED STATES ?ATENT @FFIC Application July 18, 1925,

Serial No. 44,504, and

in Canada May 11, 192 2 Claims. (01. 25027.5)

My invention relates to cathode devices and pertains to a type of such devices as are used as element in thermionic tubes or valves.

The principal object contemplated by my invention comprises producing a cathode for theremit electrons by means of alternating currents of the ordinary house lighting frequency, such as 25 or cycle. Further, to so construct such an element that when so heated no audible ripple or disturbance will be manifest in the circuit in which such tube is used.

I accomplish these an insulating member which is likewise a heat reservoir in order that this latter member may store heat and return the same to the emitting element during that part of the cycle of the alternating heating current which is of nil or low heating value.

In the figures which accompany and form a part of this specification, and in which like reference numerals designate corresponding parts throughout.

Fig. 1 illustrates a partially broken and sectioned elevation of my device incorporated in a three element tube.

Fig. 2 illustrates diagrammatically the rela tion of my cathode with the elements of a tube, and the transformer connections therefore.

Fig. 3 illustrates an enlarged view of an alternative method of constructing my device.

Fig. 4 illustrates a partially broken and secelevation of another alternative form of my device incorporated in a three element tube.

Fig. 5 illustrates diagrammatically the relation of the parts of a three element tube Referring now to the drawing I have shown in Figs. 1 and 2 one embodiment of my device incorporated in a modern three element tube. The glass envelope 1 is shown sectioned and broken to show the plate 2, which is likewise broken to show the grid 3 and my novel cathode which consists of an insulating and heat absorbing cylinder 4 which may be made of porcelain or lava or other similar substance and wh ch supports the electron emitting filament 5. This member may be in the form of a filament or strip and is referably placed in close contact with the member 4.. The emitting member may be of any of the well known substances of high electron emissivity such as tungsten or thoriated tungsten. Obviously the cylinder 4 may be supported directly from the which passes through the press 6 and acts as one terminal for the filament. The other extremity of the filament likewise passes through the press and as shown in Fig. 2 these terminals are connected to the terminals of the secondary of a transformer 8, the primary of which is connected to any commercial alternating current source. ihe ratio of the windings of the transformer are of course such as to provide the proper voltage for the type of filament used. The relation of my cathode to the elements of the tube are as shown in Fig. 2 which diagrammatically shows the plate 2 and grid 3 in their relation to each other and the cathode 4-5. A source of potent al 9 and a signal receiving device 10 are shown in their proper relation to the plate 2. In the operation of the device, the filament 5 when heateddue to alternating current from the transformer 8 emits a fiow of electrons to the plate 2 due to the positive potential applied by the battery 9. Heat of the applied alternating current it returns heat both by radiation and conduction to the filament to cause the filament to maintain a substantially constant temperature.

Fig. 3 illustrates an enlarged View of an alternative method of disposing the electron emissive member on the cylinder. In this form the filament 12 is wound bifilar and is disposed 1ongitudinally alternately on the outer and inner surfaces of the cylinder 13 in toroidal form. This form of winding is non-inductive and hence produces no electromagnetic field which might cause disturbances to the operation of the device. Further, the mid-point of the filament is connected to a lead wire 14 which with the two extremities of the filament pass through the press and are adapted to be connected to a transformer as will be hereinafter explained.

In Figs. 4; and 5 I have illustrated a further modification of my device. In this form the plate 20 and grid 21 are similar to that of Figs. 1 and 2 while the cathode comprises a cylinder 22 of similar construction to that hereinbefore referred to with the emissive member 23 wound helically thereon in bifilar form. The mid-point is connected to a lead member 24 which acts as a support for the cylinder. In Fig. 5 a source of positive potential 25 is shown connected to the plate 20 and a signal receiving means 26 is included in the plate circuit. The extremities of the filament 23 are connected to the terminals of a potentiometer 27 which is connected across the secondary of a transformer 28 the primary of which is connected to a source of alternating current. The mid-point of the filament is connected through conductor 24 to a sliding contact on the potentiometer and this contact may be adjusted so that equal currents of opposite polarity traverse the conductor 24. The conductor 24 is thus at zero potential and carries no current and hence when the plate return is connected thereto as shown no disturbing potentials enter the plate circuit. Likewise when the grid'return is connected to the conductor 24 no disturbances due to fluctuation voltages occur in the grid circuit. The bifilar disposition of the filament prevents any disturbance through the elimination of an electro-magnetic field.

From the foregoing it will be observed that I have produced a novel form of cathode in which alternating currents of commercial frequency may be used as a source of heat without causing any disturbance to the normal operation of the thermionic tube in which such cathode is used. That the device is simple to construct and that it may therefore be made easily and cheaply.

I claim:

1. An audion tube including an electrode com prising a tubular heat absorbing member of insulating material, a member adapted to emit electrons when heated by alternating current passing therethrough, said emitting member being spirally arranged about said absorbing member in intimate engagement therewith to heat said absorbing member by both radiation and conduction during flow of current therethrough and receive heat from said absorbing member at the nil point 01" current flow through said emitting member whereby said emitting member is maintained at a substantially constant temperature by the fiow of alternating current therethrough, the return conductor from one end of said spirally arranged emitting member being positioned within said tubular member, a grid electrode positioned around and away from said emitting member, and a plate electrode positioned around and away from said grid electrode.

2. A cathode for audion tubes comprising a tubular heat absorbing member of insulating material, a member adapted to emit electrons when heated by alternating current passing therethrough, said emitting member being spirally arranged about said absorbing member in intimate engagement therewith to heat said absorbing member by both radiation and conduction during flow of current therethrough and receive heat 1 from said absorbing member at the nil point of current flow through said emitting member whereby said emitting member is maintained at a substantially constant temperature by the flow of alternating current therethrough, said emitting member passing through the wall of said supporting member adjacent to one end thereof and returning through said supporting member.

FREDERICK S. MCCULLOUGH. 

